Imaging in curved arrays: methods to produce free-formed curved detectors

ABSTRACT

A detector including a detector membrane comprising a semiconductor sensor and a readout circuit, the detector membrane having a thickness of 100 micrometers or less and a curved surface conformed to a curved focal plane of an optical system imaging electromagnetic radiation onto the curved surface; and a mount or substrate attached to a backside of the detector membrane. A maximum of the strain experienced by the detector membrane is reduced by distribution of the strain induced by formation of the curved surface across all of the curved surface of the detector membrane, thereby allowing a decreased radius of curvature (more severe curving) as compared to without the distribution.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(e) of commonlyassigned U.S. Provisional Patent Application Ser. No. 62/902,563, filedSep. 19, 2019, by Todd J. Jones and Shouleh Nikzad, entitled “IMAGING INCURVED ARRAYS: METHODS TO PRODUCE SPHERICALLY CURVED DETECTORS,”(CIT-8346-P), which application is incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under Grant No.80NM0018D004 awarded by NASA (JPL). The government has certain rights inthe invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to detectors and methods of making thesame.

2. Description of the Related Art

Conventional infrared imaging cameras are bulky due to complicatedoptics required to flatten their focal plane, as illustrated in FIG. 1A.The ability to curve the detector array eliminates most of the opticalcomponents making up that bulk. However, conventional attempts to curvedetector membranes are limited to pneumatic forming or direct contactwith forceful molds. These methods cause high stresses which limit thedegree of curvature of the detector array. What is needed are improvedmethods for conforming the detector array to the focal plane withoutimparting undesirable strain to the detector array. The presentinvention satisfies this need.

SUMMARY OF THE INVENTION

Devices and methods according to embodiments described herein include,but are not limited to, the following.

1. A detector, comprising:

a detector membrane comprising a semiconductor sensor and a readoutcircuit, the detector membrane having a thickness of 100 micrometers orless and a curved surface conformed to a curved focal plane of anoptical system imaging electromagnetic radiation onto the curvedsurface; and

a mount attached to a backside of the detector membrane; wherein:

a maximum of the strain experienced by the detector membrane is reducedby distribution of the strain induced by formation of the curved surfaceacross all of the curved surface of the detector membrane, therebyallowing a decreased radius of curvature of the curved surface, and

the semiconductor sensor converts photons to charged particles and thereadout circuit measures a quantity of the charged particles, thesemiconductor comprises an elemental semiconductor or compoundsemiconductor and the readout circuit is integrated with thesemiconductor sensor monolithically or in a hybrid fashion.

2. The detector of example 1, wherein an adhesion between the mount andthe detector membrane distributes the strain.

3. The detector of example 1 or 2, wherein the semiconductor comprisessilicon or a group III-V semiconductor, II-VI semiconductor, and thesemiconductor sensor or focal plane array detects electromagneticradiation having a wavelength in a range of 400 nm-16 microns.

4. The detector of example 1, 2, or 3 wherein:

the detector membrane has a radius of curvature of 50 mm or less, and

the curved surface has an area receiving electromagnetic radiation of atleast 400 millimeters; and the mathematical ratio of the radius ofcurvature in millimeters divided by the square root of the curvedsurface area taken in millimeters squared is less than 2.5.

5. The detector of one or any combination of the claims 1-3, wherein thecurved surface is spherical, parabolic, elliptical, or custom designedshape.

6. A wearable infrared imager or a camera comprising the detector of anyof the claims 1-4.

7. A detector, comprising:

a detector membrane comprising a semiconductor sensor and a readoutcircuit, the detector membrane having a thickness of 100 micrometers orless and a curved surface conformed to a curved focal plane of anoptical system imaging electromagnetic radiation onto the curvedsurface; wherein:

the semiconductor sensor converts photons to charged particles and thereadout circuit measures a quantity of the charged particles, thesemiconductor comprises an elemental semiconductor or compoundsemiconductor and the readout circuit is integrated with semiconductorsensor monolithically or in a hybrid fashion;

the detector membrane a radius of curvature of 50 mm or less; and

the curved surface has an area of at least 400 millimeters squared; and

the mathematical ratio of the radius of curvature in millimeters dividedby the square root of the curved surface area taken in millimeterssquared is less than 2.5.

8. A method of making a curved detector, comprising:

obtaining a detector membrane comprising a semiconductor having athickness less than 100 microns;

applying one or more forces at a plurality of locations on the detectormembrane and in one or more directions, the one or more forces deformingthe detector membrane so as to form a curved surface of the detectormembrane, wherein:

the forces applied in one direction are applied a frictionless mannerwith no friction between the detector membrane and the actuator applyingthe forces, or

when the one or more directions include a plurality of directions, thedirections include one or more lateral directions in a tangential planeof a surface of the detector membrane;

progressively attaching the detector membrane to a mount as the forcesare applied so that the mount sustains or supports a majority of thestrain, wherein the detector membrane is adhered to an adhesive on asurface of the mount, the surface having the desired/designed/targetradius of curvature of the curved surface.

9. The method of example 8, further comprising physically contacting thedetector membrane to a flexible actuator membrane generating the forcesand applying the one or more forces to the detector membrane via aphysical contact between the actuator membrane and the detectormembrane.

10. The method of example 9, wherein:

the flexible actuator membrane comprises a plurality of concentricconductors in a plane of the flexible actuator membrane, and

applying the forces comprises:

passing an electrical current in the conductors, and

applying a magnetic field to induce a Lorentz force on the conductorsthat laterally stretches or contracts the flexible actuator membrane,thereby delivering through the physical contact the one or more forcescomprising a radial force inwards or outwards.

11. The method of example 9, wherein:

the flexible actuator membrane comprises two layers each including aplurality of concentric fluidic channels in a plane of the flexibleactuator membrane; and

applying the forces comprises controlling a pressure of a fluid in thefluidic channels causing the flexible actuator membrane to expand orcontract, thereby delivering through the physical contact the one ormore forces comprising a radial force inwards or outwards.

12. The method of example 8, further comprising:

physically contacting the detector membrane with a flexible actuator orflexible actuator membrane (e.g., bimetallic plate) comprising at leasttwo materials having different coefficients of thermal expansion; and

heating and/or cooling the flexible actuator membrane to a plurality oftemperatures causing the bimetallic plate to deform and applying the oneor more forces to the detector membrane via a physical contact betweenthe bimetallic plate and the detector membrane.

13. The method of example 8, wherein applying the forces comprisessequentially heating or cooling the detector membrane whileprogressively attaching the detector membrane to the mount having thedesired radius of curvature, so as to seize the detector membrane uponthe surface of the mount when the detector membrane is thermallystressed to an optimal strain for a given region of contact between thedetector membrane and the mount.

14. The method of example 8, further comprising applying a heatshrinking polymer to the detector membrane, wherein applying the forcescomprises warming, to various degrees, only those regions of thedetector membrane of specified radius from the center of the detectormembrane.

15. The method of example 8, further comprising applying the one or moreforces using concentrically arrayed piezo electric actuators on aflexible material, wherein:

the piezo electric actuators are set against a stiff platform at one endopposite the detector membrane and are attached to the detector membraneat the other of their ends, and

the flexible material between the piezo electric actuators allows thepiezo electric actuators to tilt laterally during their longitudinaldeformations.

16. The method of example 8, further comprising: physically contacting anested set of concentric cylinders to the detector membrane, thecylinders each having a different radius; and

displacing each of the cylinders against the detector membrane so thatthe cylinders transfer the one or more forces deforming the detectormembrane with increasing extent with larger radius of cylinder.

17. The method example 16, wherein the nested cylinders are graduallydisplaced with a curved profile.

18. The method of example 8, further comprising progressively attachingthe detector membrane to the mount using a frame supporting anelastomer, the elastomer patterned with fingers or a web and the fingersor the web providing a reversible soft contact between the detectormembrane and the frame.

19. The method of example 18, further comprising:

(a) depositing the elastomer on the detector membrane;

(b) lithographically patterning the elastomer with the web or fingerstructures, wherein the patterned elastomer is supported in a frame; and

20. The method of any of the claims 7-18 further comprising manipulatingthe detector membrane using the frame while the detector membrane isbeing deformed using one or more different methods.

21. The method of example 7, wherein the curved surface is formed usinga combination of the methods of claims 8-17.

22. An apparatus, comprising:

an actuator having structures (e.g., piezo actuators, concentricconductors, fluidic channels, nested cylinders) positioned to apply oneor more forces at a plurality of locations on the detector membrane andin one or more directions, the one or more forces deforming the detectormembrane so as to form a curved surface of the detector membrane,wherein:

-   -   the forces applied in one direction are applied a frictionless        manner with no friction between the detector membrane and the        actuator applying the forces, or    -   when the one or more directions include a plurality of        directions, the directions include one or more lateral        directions in a tangential plane of a surface of the detector        membrane; and

a mount positioned to progressively attach to the detector membrane asthe forces are applied so that the mount sustains or supports a majorityof a strain induced in the detector membrane by the forces, wherein thedetector membrane is attached to a surface of the mount having a radiusof the curved surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1A-1B. Comparison of state-of-the-art flat imagers to curvedimagers, wherein FIG. 1A illustrates a flat imager and FIG. 1Billustrates a curved imager according to one or more embodimentsdescribed herein.

FIG. 2 . Schematic illustrating an apparatus for manufacturing a curvedimager.

FIG. 3A-3B. Schematics illustrating the apparatus for making a curvedimager using a magnetic field, wherein FIG. 3A is a side view and FIG.3B is a top view of the actuator membrane.

FIG. 4A-4E. Schematics illustrating the apparatus for making a curvedimager using a pressure or vacuum conforming, wherein FIG. 4A is a sideview, FIG. 4B is a top view of the actuator membrane, FIG. 4C shows theevolution of CCD flatness using pressure conforming, FIG. 4D shows theevolution of flatness using vacuum conforming and FIG. 4E shows theresulting detector array on a curved substrate.

FIG. 5 . Schematic illustrating the apparatus for making a curved imagerusing piezo actuators.

FIG. 6A-6C. Schematic illustrating the apparatus for making a curvedimager using cylinders, wherein FIG. 6A is a side view, FIG. 6B is a topview, and FIG. 6C is a perspective view.

FIG. 7 . Schematic illustrating the apparatus for making a curved imagerusing bimetallic layers.

FIG. 8 . Schematic illustrating the apparatus for making a curved imagerusing heating elements.

FIG. 9 . Schematic illustrating the apparatus for making a curved imagerusing heat shrinking polymer.

FIG. 10 . Schematic illustrating the apparatus for making a curvedimager using air pressure.

FIG. 11 illustrates results of strain modeling for forming the curveddetector membranes using hydrostatic pressure using the apparatus ofFIG. 3A.

FIG. 12 illustrates results of strain modeling for forming the curveddetector membrane using a full contact with as sphere using theapparatus of FIG. 6B.

FIG. 13 plots sharpest radius of curvature as a function of square arrayside such that strain is 0.01.

FIG. 14 . Frame comprising patterned elastomer for manipulating thedetector membrane.

FIG. 15A-15B illustrates curved detector arrays characterized in FIG. 15, wherein FIG. 15A is a top view and FIG. 15B is a side view schematic.

FIG. 16A-16C plots the performance of the curved detectors of FIG. 15 ,for ROC of 500 mm (FIG. 16A), 400 mm (FIG. 16B) and 250 mm (FIG. 16C).

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Technical Description

1. Example Imager

FIG. 1B illustrates an imager 100 comprising an optical system 101having a non-planar focal plane 150, and a detector membrane 102. Thedetector membrane comprises a semiconductor comprising a sensor 103(semiconductor sensor, e.g., comprising array of pixels or sensorregions), optionally a readout circuit, and a free-formed or curvedsurface 106 conformed to (or matched to) a curved focal plane 150 of theoptical system imaging electromagnetic radiation 108 onto the curvedsurface. In one or more examples, the detector membrane has a thicknessT of 100 micrometers or less (e.g., in a range of 1-100 micrometers).

FIG. 4E illustrates the imager further comprises a mount 400 attached toa backside 402 of the detector membrane; wherein a maximum of the strainexperienced by the detector membrane is reduced by distribution of thestrain, induced by formation of the curved surface, across all of thecurved surface of the detector membrane, thereby allowing a decreasedradius of curvature (more curving or more severe curving) of the curvedsurface as compared to without the distribution.

The sensor (or semiconductor sensor) converts photons to chargedparticles and the readout circuit measures a quantity of the chargedparticles. The readout circuit is integrated with semiconductor sensormonolithically or in a hybrid fashion. In one or more examples, areadout circuit integrated in a hybrid fashion means the readout circuitis manufactured separately or as a separate element or component andthen mated or attached to the semiconductor sensor. In one or moreexamples, the readout circuit converts charge to voltage.

The semiconductor or semiconductor sensor comprises or consistsessentially of an elemental semiconductor (e.g., silicon) or compoundsemiconductor (e.g., group II-VI semiconductor). For example, thesemiconductor may comprise/consist essentially of at least one ofsilicon, a group III-V semiconductor, or group II-VI semiconductor. Thesensor may detect electromagnetic radiation having a wavelength in arange of 400 nm-16 microns.

In various examples, the adhesion between the mount and the detectormembrane distributes the strain.

In one or more examples, the detector membrane has a radius of curvatureof 50 mm or less; and the curved surface has an area of at least 400millimeters squared.

2. Example Manufacturing Method and Apparatus

The present disclosure further describes methods and systems formanufacturing curved detector arrays (or detector arrays having surfacesconformed to any desired focal plane shape). In a first step, asemiconductor comprising a detector chip and any hybridized readoutchips is thinned. Depending on the required radius of curvature, thefinal thickness can be a membrane less than 50 micrometers thick. Themembranes are fragile and cannot sustain significant strain. Thus, theproduction of a curve membrane depends on delivering the forces neededto shape the brittle membrane in a way that does not exceed the weakeststrain limit of the semiconductor crystals which the detector is madeof.

FIGS. 2-10 illustrate a method of making a curved detector, comprising(a) obtaining (or thinning) a detector membrane 102 comprising asemiconductor having a thickness less than 100 microns; applying one ormore forces at a plurality of locations on the detector membrane and inone or more directions, the one or more forces deforming the detectormembrane so as to form a curved surface of the detector membrane; andprogressively attaching the detector membrane to a mount as the forcesare applied so that the mount sustains or supports a majority of thestrain. The detector membrane is adhered to an adhesive on a surface ofthe mount, and the surface of the mount has the desired/designed/targetradius of curvature of the curved surface. In one or more examples, thecurved surface (and the surface of the mount) comprise a sphericalsurface, e.g., a section of surface of a sphere, a parabolic surface, oran elliptical surface, or custom designed shape.

In various examples, the adhesive 306 on the mount is selectivelyphotoactivated at different regions of the mount in order to achieve theprogressive attachment/adhesion between the detector membrane and themount. In various examples, the photoactivated adhesive isphotoactivated by shining electromagnetic radiation through the mountthat is transparent.

In one or more examples, the forces applied are applied in one directionand are applied a frictionless manner with no friction between thedetector membrane and the actuator applying the forces (e.g., using alubricant or the naturally frictionless surfaces of the detector andactuator). In other examples, when the one or more directions include aplurality of directions, the directions include one or more lateraldirections in a tangential plane of a surface of the detector membrane.

FIG. 2 further illustrates an apparatus for making a curved or conformaldetector, comprising an actuator 300 or plate including structures 302for applying the one or more forces to the detector membrane. Thestructures are actuated and positioned so that the forces form a curvedsurface of the detector membrane (or a surface conformed or matched tothe focal plane of the imager). FIG. 2 further illustrates the mount 400positioned or configured to progressively or gradually attach to thedetector membrane as the forces are applied.

In one or more examples, the lateral forces are increased as a functionof increasing radial distance from the center of the detector membrane.

In one or more examples, thinned membranes can be conformed tosubstrates for flat or curved focal planes or free form surfaces andreal time adjustment of curvature is possible with no substrateattachment.

3. Example Manufacturing Methods

FIGS. 3A and 3B illustrate an example wherein the curvature is attainedby attaching the detector membrane to a flexible actuator membranecomprising the structures including embedded concentric conductors(e.g., traces). An intense perpendicular magnetic field drives thecurrent carrying concentric conductors laterally to stretch or contractthe detector membrane (according to principle of a Lorentz force on awire). Similar flexible conductor membrane structures have been used inloudspeaker designs, such as the Heil Air-Motion Transformer. In one ormore examples, the current is DC so as to deliver a steady radial forceinward or outward as needed. The gently delivered deformation is createdagainst the mount comprising the waiting spherical mount for permanentadhesion.

FIGS. 4A and 4B illustrate an example wherein the flexible actuatormembrane contains two layers of structures comprising concentricmicro-fluidic channels. In the example of FIG. 4A, the pressure isadjusted so that the fluidic channels in the outer layer (furthest fromthe detector membrane) expand while the channels in the inner layer(closest to the detector membrane) contract, so as to form the curvedsurface. In one example, the PDMS polymer of the micro fluidic structureis stretchy and expands under pressure. Adjusting the pressure (orvacuum) in each layer generates a gentle curving force against theattached detector membrane. FIG. 4C shows the evolution of CCD flatnessusing pressure conforming and FIG. 4D shows the evolution of flatnessusing vacuum conforming. FIG. 4E shows the resulting detector arraymounted on a curved substrate.

FIG. 5 illustrates an example wherein the structures delivering a steadydeliberate force comprise concentrically arrayed piezo electricactuators. The piezos are set against a stiff disk at one of their endsand are softly attached to the detector membrane at the other. There issufficient flexible material between the piezos to allow the piezos totilt laterally during their longitudinal deformations.

FIG. 6A illustrates an example comprising softly attaching thestructures comprising a nested set of concentric cylinders which can beacted upon with gentle force at one end and allowed to deform thedetector membrane with increasing extent with larger radius of cylinder.This method can benefit from having a contrasting set of cylinders onthe opposite side of the detector membrane. Especially unique to thisapproach would be making the assembly so the contact to the detectormembrane is nearly frictionless. This allows the membrane to adjustlaterally to its natural minimum of stored mechanical energy. FIG. 6B atop view of the nested cylinders and FIG. 6C shows attachment of animager to a cylindrical backing.

FIG. 7 illustrates example attaching a custom bi-metallic plate whichdeforms to a known degree of curvature for each temperature the plate isexposed to.

FIG. 8 illustrates an example wherein the structure comprises heatingelements sequentially heating or cooling the detector membrane duringits gradual application to a waiting spherical mount. The apparatusseizes the membrane upon the mount (e.g., a sphere) when the detectormembrane is thermally stressed to the optimal strain for the givenregion of contact.

FIG. 9 illustrates another approach comprising applying a heat shrinkingpolymer (e.g., polyolefin, PVC, polyethylene, polypropylene) andwarming, to various degrees, only those regions of the detector arrayhaving a specified radius from the center of the array.

FIG. 10 illustrates freestanding thinned membrane comprising 1000×1000pixel CCDs curved to different curvatures using air pressure. The CCDwas taken from essentially flat configuration to ˜250 mm radius ofcurvature (ROC) with no observed mechanical damage.

In one or more examples, a combination of the above described methodscan be used to simultaneously act upon the detector membrane and producethe final curvature.

Strain Modeling

In one or more examples, the manufacturing uses a model of the expectedstrain of a spherically curved detector membrane when it has beendeformed by purely orthogonal forces. The analysis includesconsideration of creating less strain (than is created using orthogonalforces) by means of lateral forces in the plane of the detectormembrane. As described herein, the method can include applying lateralforce in the progression from flat to final curve and progressivelyseizing the membrane as the radius of contact increases, so as to formthe detector membrane into a final artificial state of straindistribution lower that its natural state by virtue of the adhesiveforces which sustain the lateral strain.

FIG. 11 illustrates results of strain modeling for forming the curveddetector membranes using hydrostatic pressure, for a membrane radius=2mm, membrane thickness H=5 micrometers, and an applied pressure=5* Youngmodulus, e.g., using the apparatus of FIG. 3A.

FIG. 12 illustrates results of strain modeling for forming the curveddetector membrane using a full contact with as sphere, for a membraneradius=2 mm, membrane thickness H=5 micrometers.

FIG. 13 illustrates an example of conforming a thinned silicon detectormembrane by mapping a square array onto a spherical substrate andplotting the sharpest radius of curvature (ROC) for a given area tomaintain 0.01 (1%) strain. This strain allows staying well below theideal elastic limit of silicon which is theoretically 17% (Reference: D.Roundy, M. L. Cohen, Ideal strength of diamond, Si, and Ge. Phys. Rev. B64, 212103 (2001), incorporated by reference herein). Under this strainas shown in FIG. 13 , smaller arrays accommodate tighter ROCs, largerarrays require gentler ROCs. By taking advantage of the lessconservative silicon elastic limit of 17%, even monolithic detectors canaccommodate smaller ROCs. Clearly, mosaicking multiple detectors canalso accommodate a larger range of ROCs. Methods described herein allowthe application of higher strain up to the elastic limit (e.g., in therange of 0.01-17%).

Contacting the Membranes

Various methods for softly contacting and mounting the detectormembranes can be used. In one example, the mount progressively attachingto the detector membrane comprises naturally clingy polymers or UV cureepoxies patterned with delicate fingers or ‘spider webs’ that seize thedetector membrane. The transition from thinning of a thick detectorstack or ‘sandwich’ to curving the thinned detector membrane may alsoinvolve a strategic release of the detector membrane from a rigidsubstrate over to a flexible carrier.

FIG. 14 illustrates a frame supporting an elastomer, the elastomerpatterned with fingers or a web and the fingers or the web providing areversible soft contact between the detector membrane and the frame. Theframe is used to progressively attach the detector membrane to the mountand/or manipulate the detector membrane while the detector membrane isbeing deformed using one or more different methods (including one ormore of, or a combination of the methods) described herein (see e.g.,methods of FIG. 2-10 ).

In one or more examples, the frame and elastomer is fabricated by (a)depositing the elastomer on the detector membrane; and (b)lithographically patterning the elastomer with the web or fingerstructures, wherein the patterned elastomer is supported in a frame.

In various examples, the fingers or web comprise a polymer (e.g., UVcurable epoxy, PVA poly vinyl acetate).

Detector Characterization

FIG. 15A illustrates a 1000×1000 pixel, 12 μm thick detector membranecomprising charge coupled devices CCDs or a focal plane array attachedto curved substrates and having a ROC=250 mm. The freestanding detectormembranes curved using air pressure. For comparison, FIG. 15A alsoillustrates the same CCD formats attached to flat substrates. The changein diffraction pattern observed on the detector surfaces evidences thespherical curvature. FIG. 15B illustrates the structure of the detectormembrane comprises CCDs (silicon p-n junctions) and a delta doped layernear the surface receiving the photons (for passivation).

The curved focal plane arrays (CFPA) of FIG. 15A were operated andoutput current was measured as a function light intensity for CFPAs withthree different radius of curvature (ROC), as shown in FIG. 16 . Nochange in the signal level or device behavior was observed as a functionof curvature.

Applications

Conventional imaging systems produce a flat focal plane wave front inorder to be captured by a flat imaging array. However, very simpleimaging optics produce non-planar focal surfaces. If the imagingdetector can be shaped to the non-planar focal surface, as describedherein, then there is no need for complicated optics. The savings incost, size, and mass of the optical system enables new applications ofthe imaging system.

Furthermore, the curved detector array enables a larger field of viewand reduces aberrations such as astigmatism and coma, and increasesperipheral brightness and sharpness. In the natural world mammalian eyesexhibit the value the design: simple lens and curved retina.

For space applications, the curved detector array enables lighter andmore compact cameras for satellites and rovers. Imaging systems using acompact curved detector manufactured using processes described hereincan be used for wearable IR imaging and low mass and volume systems.Examples include, but are not limited to, consumer cameras and smartphones, and headwear for the military and firefighters.

Device and Method Embodiments

Devices and methods according to embodiments described herein include,but are not limited to, the following.

1. FIG. 1B illustrates a detector, comprising:

a detector membrane comprising a semiconductor sensor and a readoutcircuit, the detector membrane having a thickness of 100 micrometers orless and a curved surface conformed to a curved focal plane of anoptical system imaging electromagnetic radiation onto the curvedsurface; and

a mount attached to a backside of the detector membrane; wherein:

a maximum of the strain experienced by the detector membrane is reducedby distribution of the strain induced by formation of the curved surfaceacross all of the curved surface of the detector membrane, therebyallowing an increased radius of curvature of the curved surface, and

the semiconductor sensor converts photons to charged particles and thereadout circuit measures a quantity of the charged particles, thesemiconductor comprises an elemental semiconductor or compoundsemiconductor, and the readout circuit is integrated with semiconductorsensor monolithically or in a hybrid fashion.

2. The detector of example 1, wherein an adhesion between the mount andthe detector membrane distributes the strain.

3. The detector of example 1 or 2, wherein the semiconductor comprisessilicon or a group III-V semiconductor, II-VI semiconductor, and thesemiconductor sensor or focal plane array detects electromagneticradiation having a wavelength in a range of 400 nm-16 microns.

4. FIG. 1B illustrates the detector of example 1, 3, or 4 wherein thedetector membrane a radius of curvature of 50 mm or less; the curvedsurface has an area A of at least 400 millimeters squared; and themathematical ratio of the radius of curvature in millimeters divided bythe square root of the curved surface area taken in millimeters squaredis less than 2.5. In one or more examples, this mathematical ratio isbecause the key thing is the strain (not just the ROC or the area) andthe allowable ROC increases as the detector area increases (square rootof area).

5. The detector of one or any combination of the examples 1-4, whereinthe curved surface is spherical, parabolic, elliptical, or customdesigned shape.

6. A wearable infrared imager or a camera comprising the detector of anyof the examples 1-5.

7. A detector, comprising:

a detector membrane comprising a semiconductor sensor and a readoutcircuit, the detector membrane having a thickness of 100 micrometers orless and a curved surface conformed to a curved focal plane of anoptical system imaging electromagnetic radiation onto the curvedsurface; wherein:

the semiconductor sensor converts photons to charged particles and thereadout circuit measures a quantity of the charged particles, thesemiconductor comprises an elemental semiconductor or compoundsemiconductor and the readout circuit is integrated with semiconductorsensor monolithically or in a hybrid fashion;

the detector membrane a radius of curvature of 50 mm or less; and thecurved surface has an area of at least 400 millimeters squared.

8. FIG. 2 -FIG. 10 illustrate a method of making a curved detector,comprising:

obtaining a detector membrane comprising a semiconductor having athickness less than 100 microns;

applying one or more forces at a plurality of locations on the detectormembrane and in one or more directions, the one or more forces deformingthe detector membrane so as to form a curved surface of the detectormembrane, wherein:

-   -   the forces applied in one direction are applied a frictionless        manner (or substantially frictionless manner) with no friction        (or substantially no friction) between the detector membrane and        the actuator applying the forces, or    -   when the one or more directions include a plurality of        directions, the directions include one or more lateral        directions in a tangential plane of a surface of the detector        membrane;

progressively attaching the detector membrane to a mount as the forcesare applied so that the mount sustains or supports a majority of thestrain, wherein the detector membrane is adhered to an adhesive on asurface of the mount, the surface having the desired/designed/targetradius of curvature of the curved surface.

9. The method of example 8, further comprising physically contacting thedetector membrane to a flexible actuator membrane generating the forcesand applying the one or more forces to the detector membrane via aphysical contact between the actuator membrane and the detectormembrane.

11. FIG. 3A illustrates the method of example 9, wherein:

the flexible actuator membrane comprises a plurality of concentricconductors in a plane of the flexible actuator membrane, and

applying the forces comprises:

passing an electrical current in the conductors, and

applying a magnetic field to induce a Lorentz force on the conductorsthat laterally stretches or contracts the flexible actuator membrane,thereby delivering through the physical contact the one or more forcescomprising a radial force inwards or outwards.

11. FIG. 4A illustrates the method of example 9, wherein:

the flexible actuator membrane comprises two layers each including aplurality of concentric fluidic channels in a plane of the flexibleactuator membrane; and

applying the forces comprises controlling a pressure of a fluid in thefluidic channels causing the flexible actuator membrane to expand orcontract, thereby delivering through the physical contact the one ormore forces comprising a radial force inwards or outwards.

12. FIG. 7 illustrates the method of example 8, further comprising:

physically contacting the detector membrane with a flexible actuator orflexible actuator membrane (e.g., bimetallic plate) comprising at leasttwo materials having different coefficients of thermal expansion; and

heating and/or cooling the flexible actuator membrane to a plurality oftemperatures causing the bimetallic plate to deform and applying the oneor more forces to the detector membrane via a physical contact betweenthe bimetallic plate and the detector membrane.

13. FIG. 8 illustrates the method of example 8, wherein applying theforces comprises sequentially heating or cooling the detector membranewhile progressively attaching the detector membrane to the mount havingthe desired radius of curvature, so as to seize the detector membraneupon the surface of the mount when the detector membrane is thermallystressed to an optimal strain for a given region of contact between thedetector membrane and the mount.

14. FIG. 9 illustrates the method of example 8, further comprisingapplying a heat shrinking polymer to the detector membrane, whereinapplying the forces comprises warming, to various degrees, only thoseregions of the detector membrane of specified radius from the center ofthe detector membrane.

15. FIG. 5 illustrates the method of example 8, further comprisingapplying the one or more forces using concentrically arrayed piezoelectric actuators on a flexible material, wherein:

the piezo electric actuators are set against a stiff platform at one endopposite the detector membrane and are attached to the detector membraneat the other of their ends, and

the flexible material between the piezo electric actuators allows thepiezo electric actuators to tilt laterally during their longitudinaldeformations.

16. FIG. 6A illustrates the method of example 8, further comprising:

physically contacting a nested set of concentric cylinders to thedetector membrane, the cylinders each having a different radius; and

displacing each of the cylinders against the detector membrane so thatthe cylinders transfer the one or more forces deforming the detectormembrane with increasing extent with larger radius of cylinder.

17. The method example 16, wherein the nested cylinders are graduallydisplaced with a curved profile.

18. FIG. 14 illustrates the method of example 8 further comprisingprogressively attaching the detector membrane to the mount using a framesupporting an elastomer, the elastomer patterned with fingers or a weband the fingers or the web providing a reversible soft contact betweenthe detector membrane and the frame.

19. The method of example 18, further comprising:

(a) depositing the elastomer on the detector membrane;

(c) lithographically patterning the elastomer with the web or fingerstructures, wherein the patterned elastomer is supported in a frame; and

20. The method of any of the examples 8-18 further comprisingmanipulating the detector membrane using the frame while the detectormembrane is being deformed using one or more different methods.

21. The method of example 7, wherein the curved surface is formed usinga combination of the methods of examples 8-18.

22. FIG. 2 illustrates an apparatus, comprising:

an actuator having structures (e.g., piezo actuators, concentricconductors, fluidic channels, nested cylinders) positioned to apply oneor more forces at a plurality of locations on the detector membrane andin one or more directions, the one or more forces deforming the detectormembrane so as to form a curved surface of the detector membrane,wherein:

-   -   the forces applied in one direction are applied a frictionless        manner with no friction between the detector membrane and the        actuator applying the forces, or    -   when the one or more directions include a plurality of        directions, the directions include one or more lateral        directions in a tangential plane of a surface of the detector        membrane; and

a mount positioned to progressively attach to the detector membrane asthe forces are applied so that the mount sustains or supports a majorityof a strain induced in the detector membrane by the forces, wherein thedetector membrane is attached to a surface of the mount having a radiusof the curved surface.

Conclusion

This concludes the description of the preferred embodiment of thepresent invention. The foregoing description of one or more embodimentsof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not by this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A detector, comprising: a detector membranecomprising a semiconductor sensor and a readout circuit, the detectormembrane having a thickness of 100 micrometers or less and a curvedsurface conformed to a curved focal plane of an optical system imagingelectromagnetic radiation onto the curved surface; and a mount attachedto a backside of the detector membrane; wherein: a maximum of a strainexperienced by the detector membrane is reduced by distribution of thestrain induced by formation of the curved surface across all of thecurved surface of the detector membrane, thereby allowing an increasedradius of curvature of the curved surface, and the semiconductor sensorconverts photons to charged particles and the readout circuit measures aquantity of the charged particles, the semiconductor sensor comprises anelemental semiconductor or compound semiconductor, and the readoutcircuit is integrated with the semiconductor sensor monolithically or ina hybrid fashion.
 2. The detector of claim 1, wherein an adhesionbetween the mount and the detector membrane distributes the strain. 3.The detector of claim 1, wherein the elemental semiconductor or thecompound semiconductor comprises silicon or a group III-V semiconductor,or a group II-VI semiconductor, and the detector membrane detectselectromagnetic radiation having a wavelength in a range of 400 nm -16microns.
 4. The detector of claim 1, wherein: the detector membrane hasa radius of curvature of 50 mm or less, and the curved surface has anarea receiving the electromagnetic radiation of at least 400millimeters.
 5. The detector of claim 1, wherein the curved surface isspherical, parabolic, elliptical, or a custom designed shape.
 6. Awearable infrared imager or a camera comprising the detector of claim 1.7. A detector, comprising: a detector membrane comprising asemiconductor sensor and a readout circuit, the detector membrane havinga thickness of 100 micrometers or less and a curved surface conformed toa curved focal plane of an optical system imaging electromagneticradiation onto the curved surface; wherein: the semiconductor sensorconverts photons to charged particles and the readout circuit measures aquantity of the charged particles, the semiconductor sensor comprises anelemental semiconductor or compound semiconductor and the readoutcircuit is integrated with the semiconductor sensor monolithically or ina hybrid fashion; the detector membrane comprises a radius of curvatureof 50 mm or less; and the curved surface has an area of at least 400millimeters squared.
 8. The detector of claim 1, further comprising: thestrain having the distribution induced from applying one or more forcesat a plurality of locations on the detector membrane and in one or moredirections, the one or more forces deforming the detector membrane so asto form the curved surface of the detector membrane, wherein: the forcesapplied in one direction are applied a frictionless manner with nofriction between the detector membrane and an actuator applying theforces, or when the one or more directions include a plurality ofdirections, the directions include one or more lateral directions in atangential plane of a surface of the detector membrane; the mount isprogressively attached to the detector membrane as the forces areapplied so that the mount sustains or supports a majority of the strain,wherein the detector membrane is adhered to an adhesive on a mountsurface of the mount, the mount surface having a desired/designed/targetradius of curvature of the curved surface.
 9. The detector of claim 8,further comprising the actuator comprising a flexible actuator membranegenerating the forces and applying the one or more forces to thedetector membrane via a physical contact between the flexible actuatormembrane and the detector membrane.
 10. The detector of claim 9,wherein: the flexible actuator membrane comprises a plurality ofconcentric conductors in a plane of the flexible actuator membranepositioned so that: applying the forces comprises: passing an electricalcurrent in the concentric conductors, and applying a magnetic field toinduce a Lorentz force on the concentric conductors that laterallystretches or contracts the flexible actuator membrane, therebydelivering through the physical contact the one or more forcescomprising a radial force inwards or outwards.
 11. The detector of claim9, wherein: the flexible actuator membrane comprises two layers eachincluding a plurality of concentric fluidic channels in a plane of theflexible actuator membrane positioned so that applying the forcescomprises controlling a pressure of a fluid in the concentric fluidicchannels causing the flexible actuator membrane to expand or contract,thereby delivering through the physical contact the one or more forcescomprising a radial force inwards or outwards.
 12. The detector of claim8, wherein: the actuator comprises a flexible actuator membranecomprising a bimetallic plate comprising at least two materials havingdifferent coefficients of thermal expansion, such that heating and/orcooling the flexible actuator membrane to a plurality of temperaturescauses the bimetallic plate to deform and applies the one or more forcesto the detector membrane via a physical contact between the bimetallicplate and the detector membrane.
 13. The detector of claim 8, whereinthe distribution of the strain is induced from applying the forcescomprising sequentially heating or cooling the detector membrane whileprogressively attaching the detector membrane to the mount having thedesired/designated/target radius of curvature, so as to seize thedetector membrane upon the surface of the mount when the detectormembrane is thermally stressed to an optimal strain for a given regionof contact between the detector membrane and the mount.
 14. The detectorof claim 8, further comprising a heat shrinking polymer applied to thedetector membrane, wherein applying the forces comprises warming, tovarious degrees, only those regions of the detector membrane ofspecified radius from the center of the detector membrane.
 15. Thedetector of claim 8, wherein the distribution of the strain is inducedby applying the one or more forces using concentrically arrayed piezoelectric actuators on a flexible material, wherein: the concentricallyarrayed piezo electric actuators are set against a stiff platform at oneend opposite the detector membrane and are attached to the detectormembrane at the other of their ends, and the flexible material betweenthe concentrically arrayed piezo electric actuators allows theconcentrically arrayed piezo electric actuators to tilt laterally duringtheir longitudinal deformations.
 16. The detector of claim 8, furthercomprising: a nested set of concentric cylinders physically contacted tothe detector membrane, the concentric cylinders each having a differentradius; and each of the concentric cylinders positioned so thatdisplacing the concentric cylinders against the detector membranetransfers the one or more forces deforming the detector membrane withincreasing extent with larger radius of cylinder.
 17. The detector claim16, wherein the nested set of concentric cylinders are positioned sothat the concentric cylinders may be gradually displaced with a curvedprofile.
 18. The detector of claim 8, further comprising the detectormembrane progressively attached to the mount using a frame supporting anelastomer, the elastomer patterned with fingers or a web and the fingersor the web providing a reversible soft contact between the detectormembrane and the frame.
 19. The detector of claim 18, furthercomprising: (a) the elastomer deposited on the detector membrane; (b)the elastomer lithographically patterned with the web or fingerstructures, wherein the patterned elastomer is supported in the frame.20. The detector of claim 17, comprising a frame manipulating thedetector membrane while the detector membrane is being deformed usingone or more different methods.